The present invention is in the field of braking systems. More specifically this invention relates to the piston assembly for use in a braking system.
In a braking system that has a piston or pistons applying pressure on a pressure plate via a forwardly disposed face of the piston, the piston face and the pressure plate are parallel surfaces. During braking, they encounter forces that can deflect the outer radial portions of the piston housing to cock the pistons in their housings. This action induces side loading and unnecessary stresses into the piston assembly and supporting structure Bending action increases as the brake discs wear and the piston elements must extend axially outward a greater distance for full brake application. The bending action and resultant side loading is especially harmful to assemblies that have automatic adjusters built into the pistons due to excessive wear on close clearance adjuster components, and increased difficulty in maintaining an effective seal of hydraulic fluid.
One attempt at overcoming these problems is disclosed in U.S. Pat. No. 5,205,382 by Edmisten, which is hereby incorporated by reference. This patent discloses a two-part cap with spherical mating surfaces, where the inner half of the cap mates with the forwardly disposed face of the piston, and the outer half of the cap mates with and remains parallel with the pressure plate. This allows the piston to more freely deflect with the piston housing, thus reducing side loads, and excessive wear. However, this two-part cap is difficult and expensive to manufacture.
A piston and single-piece cap are desired which would allow movement of the piston relative to the cap, so that the cap remains parallel with the pressure plate, while the piston deflects with the piston housing with minimum side loads induced into the piston and adjuster components; and which would not be difficult and expensive to manufacture.